Establishment of pregnancy requires conceptus-maternal interactions involving many hormones acting on specific receptors in the uterus. During the peri-implantation period, ovine conceptuses are bathed in endometrial secretions (histotroph). The protein components of histotroph almost certainly have a role in establishing synchrony between development of the conceptus and uterus, as well as in conceptus signaling for elongation, pregnancy recognition and implantation. Preliminary data indicate that osteopontin (OPN) is expressed and secreted by the ovine endometrium during early pregnancy in ewes. It has been hypothesized that OPN binds alphavbeta3 integrin heterodimer expressed by trophectoderm and uterus to: (1) stimulate changes in morphology of conceptus trophectoderm; and (2) induce adhesion between luminal epithelium and trophectoderm essential for attachment and placentation. The proposed studies will extend knowledge of OPN's temporal/spatial expression, hormonal regulation, receptor binding, signal transduction and effects on trophectoderm architecture during the ovine peri-implantation period.